The preceding projects have characterized opioid-selective signal transduction pathways of opioid receptors, integrin regulation of opioid receptor function and peptidase processing of endogenous opioids, using an in vitro model of cultured trigeminal neurons. The clinical studies in Sub-Project #4 complement and extend these projects by evaluating peripheral opioid pharmacology in normal and inflamed human peripheral tissue. Specifically, we propose a comprehensive series of clinical studies directly testing the hypotheses that the peripheral opioid receptor system is altered in inflamed tissue and that opioids modulate peripheral nociceptors and inflammatory pain in human pain patients. The ultimate clinical objective of these studies is to determine the neuronal mechanisms and optimal parameters for peripheral opioid analgesia in pain patients. Specific Aim 1: Characterize in humans the effects of inflammation on peripheral levels of MOR, DOR, and KOR expression and functional activity in clinical biopsies. Specific Aim 2: Determine whether receptor subtype-selective opioid agonists inhibit neurosecretion of immunoreactive substance P from peripheral terminals of human nociceptive neurons innervating normal versus inflamed human tissue biopsies. Specific Aim 3: Determine whether peripheral administration of receptor subtype-selective opioids is analgesic and/or anti-allodynic in patients experiencing spontaneous pain and mechanical allodynia in a clinical model of inflammatory pain. Specific Aim 4: Evaluate whether population characteristics are associated with altered opioid regulation of peripheral nociceptors. First, we will determine whether patients with single nucleotide polymorphisms (SNP) in the OPRM1 (A118G SNP) or OPRD1 (T921C SNP) gene have altered nociceptor responsiveness to opioid agonists; and second, we will determine whether ethnic/cultural factors associated with an underserved minority population (Hispanics) are associated with peripheral opioid pharmacology. This proposal, which includes investigations at the behavioral, biochemical and genetic levels, should greatly increase our knowledge regarding the role of peripheral opioid receptors in modulating peripheral nociceptors and pain in humans. These studies are tightly integrated with the other sub-projects and serves to independently evaluate hypotheses raised in studies using primary cultures of trigeminal neurons.